Paypal payment

Hello,
If I want to use sign-up paypal payment gateway in user man, the controller/userman must be a public address?
Now my controller RB1100 is having local ip : 172.16.x.x, user man, http:172.16.x.x/userman. I can use sign-up to go paypal but can’t recieve paypal trasaction.
Please help

Thanks
Richard